Codd's 12 rules 科德十二定律

Codd's 12 Rules/科德十二定律/コッドの12の規則

Related to Wikipedia 2016/8/2 data



準則0 The Foundation rule
For any system that is advertised as, or claimed to be, a relational data base management system, that system must be able to manage data bases entirely through its relational capabilities.
準則1 The information rule 信息準則
All information in a relational data base is represented explicitly at the logical level and in exactly one way — by values in tables.
準則2 The guaranteed access rule 保證訪問準則
Each and every data (atomic value) in a relational data base is guaranteed to be logically accessible by resorting to a combination of table name, primary key value and column name.
準則3 Systematic treatment of null values 空值的系統化處理
Null values (distinct from the empty character string or a string of blank characters and distinct from zero or any other number) are supported in fully relational DBMS for representing missing information and inapplicable information in a systematic way, independent of data type.
準則4 Dynamic online catalog based on the relational model 基於關係模型的動態的聯機數據字典
The data base description is represented at the logical level in the same way as ordinary data, so that authorized users can apply the same relational language to its interrogation as they apply to the regular data.
準則5 The comprehensive data sublanguage rule 統一的數據子語言
A relational system may support several languages and various modes of terminal use (for example, the fill-in-the-blanks mode). However, there must be at least one language whose statements are expressible, per some well-defined syntax, as character strings and that is comprehensive in supporting all of the following items:
  1. Data definition
  2. View definition
  3. Data manipulation (interactive and by program).
  4. Integrity constraints
  5. Authorization
  6. Transaction boundaries (begin, commit and rollback)
準則6 The view updating rule 視圖更新準則
All views that are theoretically updatable are also updatable by the system.
準則7 High-level insert, update, and delete 高階的插入、修改和刪除操作
The capability of handling a base relation or a derived relation as a single operand applies not only to the retrieval of data but also to the insertion, update and deletion of data.
準則8 Physical data independence 數據的物理獨立性
Application programs and terminal activities remain logically unimpaired whenever any changes are made in either storage representations or access methods.
準則9 Logical data independence 數據邏輯獨立性
Application programs and terminal activities remain logically unimpaired when information-preserving changes of any kind that theoretically permit unimpairment are made to the base tables.
準則10 Integrity independence 數據完整的獨立性
Integrity constraints specific to a particular relational data base must be definable in the relational data sublanguage and storable in the catalog, not in the application programs.
準則11 Distribution independence 分布獨立性
A relational DBMS has distribution independence.
準則12 The nonsubversion rule 無破壞準則
If a relational system has a low-level (single-record-at-a-time) language, that low level cannot be used to subvert or bypass the integrity rules and constraints expressed in the higher level relational language (multiple-records-at-a-time).